Method for transmitting or receiving channel state information in wireless communication system and device therefor

ABSTRACT

Disclosed are a method for transmitting or receiving channel state information in a wireless communication system and a device therefor. Specifically, a method for transmitting channel state information (CSI) by a terminal in a wireless communication system may comprise the steps of: receiving, from a base station, the number of antenna ports specific to one or more channel state information-reference signal (CSI-RS) resources; receiving, by the terminal, a CSI-RS on the one or more antenna ports from the base station; when the number of one or more CSI-RS resource-specific antenna ports configured in the terminal is different from the number of antenna ports in reporting units of the CSI configured in the terminal, estimating a CSI-RS antenna port on the basis of the number of antenna ports in reporting units of the CSI configured in the terminal, and deriving the CSI on the basis of the CSI-RS; and reporting the CSI to the base station.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2016/009431, filed on Aug. 25, 2016,which claims the benefit of U.S. Provisional Application No. 62/209,870,filed on Aug. 25, 2015, No. 62/210,440, filed on Aug. 26, 2015, thecontents of which are all hereby incorporated by reference herein intheir entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for transmitting or receiving channelstate information and an apparatus supporting the same.

BACKGROUND ART

Mobile communication systems have been developed to provide voiceservices, while guaranteeing user activity. Service coverage of mobilecommunication systems, however, has extended even to data services, aswell as voice services, and currently, an explosive increase in traffichas resulted in shortage of resource and user demand for a high speedservices, requiring advanced mobile communication systems.

The requirements of the next-generation mobile communication system mayinclude supporting huge data traffic, a remarkable increase in thetransfer rate of each user, the accommodation of a significantlyincreased number of connection devices, very low end-to-end latency, andhigh energy efficiency. To this end, various techniques, such as smallcell enhancement, dual connectivity, massive Multiple Input MultipleOutput (MIMO), in-band full duplex, non-orthogonal multiple access(NOMA), supporting super-wide band, and device networking, have beenresearched.

DISCLOSURE Technical Problem

An object of the present invention is proposes a method for transmittingor receiving channel state information (CSI).

Furthermore, an object of the present invention proposes a method fordetermining a CSI-RS port for deriving CSI if a CSI-RS port number foreach CSI resource for deriving CSI and a CSI-RS port number of a CSI-RSreport unit are separately defined.

Technical objects to be achieved by the present invention are notlimited to the aforementioned technical objects, and other technicalobjects not described above may be evidently understood by a personhaving ordinary skill in the art to which the present invention pertainsfrom the following description.

Technical Solution

In an aspect of the present invention, a method for a user equipment(UE) to transmit channel state information (CSI) in a wirelesscommunication system may include the steps of receiving the number ofantenna ports in each of one or more channel state information-referencesignal (CSI-RS) resources configured in the UE from an eNB, receiving,by the UE, a CSI-RS on one or more antenna ports from the eNB, derivingthe CSI based on the CSI-RS by assuming a CSI-RS antenna port based onthe number of antenna ports of a report unit of the CSI configured inthe UE, when the number of antenna ports in each of one or more CSI-RSsconfigured in the UE and the number of antenna ports of a report unit ofthe CSI configured in the UE are different, and reporting the CSI to theeNB.

In another aspect of the present invention, a UE transmitting channelstate information (CSI) in a wireless communication system includes aradio frequency (RF) unit for transmitting or receiving a radio signaland a processor controlling the RF unit, wherein the processor may beconfigured to receive the number of antenna ports in each of one or morechannel state information-reference signal (CSI-RS) resources configuredin the UE from an eNB, to receive a CSI-RS on one or more antenna portsfrom the eNB, to derive the CSI based on the CSI-RS by assuming a CSI-RSantenna port based on the number of antenna ports of a report unit ofthe CSI configured in the UE, when the number of antenna ports in eachof one or more CSI-RSs configured in the UE and the number of antennaports of a report unit of the CSI configured in the UE are different,and to report the CSI to the eNB.

Preferably, the UE may receive information of the number of antennaports of a report unit of the CSI from the eNB.

Preferably, the number of antenna ports of a report unit of the CSI maybe configured to be identical with the number of antenna ports within aspecific CSI-RS resource of the one or more CSI-RS resources configuredin the UE.

Preferably, the UE may sequentially index a total of antenna ports for atotal of CSI-RS resources configured in the UE using the number ofantenna ports of a report unit of the CSI configured in the UE.

Preferably, when a product value of the total of CSI-RS resourcesconfigured in the UE and the number of antenna ports of a report unit ofthe CSI configured in the UE is greater than a total number of antennaports for the total number of CSI-RS resources configured in the UE, theUE may request the reconfiguration of the total number of CSI-RSresources configured in the UE and/or the number of antenna ports of areport unit of the CSI configured in the UE from the eNB.

Preferably, a product value of the total of CSI-RS resources configuredin the UE and the number of antenna ports of a report unit of the CSIconfigured in the UE may be assumed to be identical with a total numberof antenna ports for the total number of CSI-RS resources configured inthe UE.

Preferably, the number of antenna ports of a report unit of the CSI maybe configured to be identical with the smallest number of antenna portsof the one or more CSI-RS resources configured in the UE.

Preferably, the number of antenna ports of a report unit of the CSI maybe configured to be identical with the greatest number of antenna portsof the one or more CSI-RS resources configured in the UE.

Preferably, the CSI may be derived with respect to only a CSI-RSresource that is identical with the number of antenna ports of a reportunit of the CSI configured in the UE among the one or more CSI-RSresources configured in the UE.

Preferably, the UE may receive the number of beams configured in the UEand the number of antenna ports of a report unit of the CSI configuredin the UE for each beam from the eNB.

Preferably, the UE may sequentially index a total of antenna ports for atotal of CSI-RS resources configured in the UE using the number ofantenna ports of a report unit of the CSI for each beam configured inthe UE.

Preferably, if the number of antenna ports of a report unit of the CSIfor the total of beams configured in the UE is greater than the totalnumber of antenna ports for the total number of CSI-RS resourcesconfigured in the UE, the UE may request the reconfiguration of thetotal number of CSI-RS resources configured in the UE and/or the numberof antenna ports of a report unit of the CSI for each beam configured inthe UE from the eNB.

Advantageous Effects

In accordance with an embodiment of the present invention, a UE cansmoothly derive CSI and feed it back to an eNB.

Furthermore, in accordance with an embodiment of the present invention,when a CSI-RS port number for each CSI resource for deriving CSI and aCSI-RS port number of a CSI-RS report unit are separately defined, anerror attributable to ambiguity between the two CSI RS port numbers canbe prevented.

Effects which may be obtained by the present invention are not limitedto the aforementioned effects, and other technical effects not describedabove may be evidently understood by a person having ordinary skill inthe art to which the present invention pertains from the followingdescription.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included herein as a part of thedescription for help understanding the present invention, provideembodiments of the present invention, and describe the technicalfeatures of the present invention with the description below.

FIG. 1 illustrates the structure of a radio frame in a wirelesscommunication system to which the present invention may be applied.

FIG. 2 is a diagram illustrating a resource grid for a downlink slot ina wireless communication system to which the present invention may beapplied.

FIG. 3 illustrates a structure of downlink subframe in a wirelesscommunication system to which the present invention may be applied.

FIG. 4 illustrates a structure of uplink subframe in a wirelesscommunication system to which the present invention may be applied.

FIG. 5 shows the configuration of a known MIMO communication system.

FIG. 6 is a diagram showing a channel from a plurality of transmissionantennas to a single reception antenna.

FIG. 7 illustrates reference signal patterns mapped to downlink resourceblock pairs in a wireless communication system to which the presentinvention may be applied.

FIG. 8 is a diagram illustrating resources to which reference signalsare mapped in a wireless communication system to which the presentinvention may be applied.

FIG. 9 illustrates a 2D-AAS having 64 antenna elements in a wirelesscommunication system to which the present invention may be applied.

FIG. 10 illustrates a system in which an eNB or UE has a plurality oftransmission/reception antennas capable of forming a 3D beam based onthe AAS in a wireless communication system to which the presentinvention may be applied.

FIG. 11 illustrates a 2D antenna system having cross-polarizations in awireless communication system to which the present invention may beapplied.

FIG. 12 illustrates a transceiver unit model in a wireless communicationsystem to which the present invention may be applied.

FIG. 13 is a diagram illustrating a method of transmitting or receivingchannel state information according to an embodiment of the presentinvention.

FIG. 14 illustrates a block diagram of a wireless communicationapparatus according to an embodiment of the present invention.

MODE FOR INVENTION

Some embodiments of the present invention are described in detail withreference to the accompanying drawings. A detailed description to bedisclosed along with the accompanying drawings are intended to describesome embodiments of the present invention and are not intended todescribe a sole embodiment of the present invention. The followingdetailed description includes more details in order to provide fullunderstanding of the present invention. However, those skilled in theart will understand that the present invention may be implementedwithout such more details.

In some cases, in order to avoid that the concept of the presentinvention becomes vague, known structures and devices are omitted or maybe shown in a block diagram form based on the core functions of eachstructure and device.

In this specification, a base station has the meaning of a terminal nodeof a network over which the base station directly communicates with adevice. In this document, a specific operation that is described to beperformed by a base station may be performed by an upper node of thebase station according to circumstances. That is, it is evident that ina network including a plurality of network nodes including a basestation, various operations performed for communication with a devicemay be performed by the base station or other network nodes other thanthe base station. The base station (BS) may be substituted with anotherterm, such as a fixed station, a Node B, an eNB (evolved-NodeB), a BaseTransceiver System (BTS), or an access point (AP). Furthermore, thedevice may be fixed or may have mobility and may be substituted withanother term, such as User Equipment (UE), a Mobile Station (MS), a UserTerminal (UT), a Mobile Subscriber Station (MSS), a Subscriber Station(SS), an Advanced Mobile Station (AMS), a Wireless Terminal (WT), aMachine-Type Communication (MTC) device, a Machine-to-Machine (M2M)device, or a Device-to-Device (D2D) device.

Hereinafter, downlink (DL) means communication from an eNB to UE, anduplink (UL) means communication from UE to an eNB. In DL, a transmittermay be part of an eNB, and a receiver may be part of UE. In UL, atransmitter may be part of UE, and a receiver may be part of an eNB.

Specific terms used in the following description have been provided tohelp understanding of the present invention, and the use of suchspecific terms may be changed in various forms without departing fromthe technical sprit of the present invention.

The following technologies may be used in a variety of wirelesscommunication systems, such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), and Non-OrthogonalMultiple Access (NOMA). CDMA may be implemented using a radiotechnology, such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented using a radio technology, such asGlobal System for Mobile communications (GSM)/General Packet RadioService (GPRS)/Enhanced Data rates for GSM Evolution (EDGE). OFDMA maybe implemented using a radio technology, such as Institute of Electricaland Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),IEEE 802.20, or Evolved UTRA (E-UTRA). UTRA is part of a UniversalMobile Telecommunications System (UMTS). 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE) is part of an Evolved UMTS(E-UMTS) using evolved UMTS Terrestrial Radio Access (E-UTRA), and itadopts OFDMA in downlink and adopts SC-FDMA in uplink. LTE-Advanced(LTE-A) is the evolution of 3GPP LTE.

Embodiments of the present invention may be supported by the standarddocuments disclosed in at least one of IEEE 802, 3GPP, and 3GPP2, thatis, radio access systems. That is, steps or portions that belong to theembodiments of the present invention and that are not described in orderto clearly expose the technical spirit of the present invention may besupported by the documents. Furthermore, all terms disclosed in thisdocument may be described by the standard documents.

In order to more clarify a description, 3GPP LTE/LTE-A is chieflydescribed, but the technical characteristics of the present inventionare not limited thereto.

General System to which the Present Invention May be Applied

FIG. 1 shows the structure of a radio frame in a wireless communicationsystem to which an embodiment of the present invention may be applied.

3GPP LTE/LTE-A support a radio frame structure type 1 which may beapplicable to Frequency Division Duplex (FDD) and a radio framestructure which may be applicable to Time Division Duplex (TDD).

The size of a radio frame in the time domain is represented as amultiple of a time unit of T_s=1/(15000*2048). A UL and DL transmissionincludes the radio frame having a duration of T_f=307200*T_s=10 ms.

FIG. 1(a) exemplifies a radio frame structure type 1. The type 1 radioframe may be applied to both of full duplex FDD and half duplex FDD.

A radio frame includes 10 subframes. A radio frame includes 20 slots ofT_slot=15360*T_s=0.5 ms length, and 0 to 19 indexes are given to each ofthe slots. One subframe includes consecutive two slots in the timedomain, and subframe i includes slot 2i and slot 2i+1. The time requiredfor transmitting a subframe is referred to as a transmission timeinterval (TTI). For example, the length of the subframe i may be 1 msand the length of a slot may be 0.5 ms.

A UL transmission and a DL transmission I the FDD are distinguished inthe frequency domain. Whereas there is no restriction in the full duplexFDD, a UE may not transmit and receive simultaneously in the half duplexFDD operation.

One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols in the time domain and includes a pluralityof Resource Blocks (RBs) in a frequency domain. In 3GPP LTE, OFDMsymbols are used to represent one symbol period because OFDMA is used indownlink. An OFDM symbol may be called one SC-FDMA symbol or symbolperiod. An RB is a resource allocation unit and includes a plurality ofcontiguous subcarriers in one slot.

FIG. 1(b) shows frame structure type 2.

A type 2 radio frame includes two half frame of 153600*T_s=5 ms lengtheach. Each half frame includes 5 subframes of 30720*T_s=1 ms length.

In the frame structure type 2 of a TDD system, an uplink-downlinkconfiguration is a rule indicating whether uplink and downlink areallocated (or reserved) to all subframes.

Table 1 shows the uplink-downlink configuration.

TABLE 1 Uplink- Down- Downlink-to- link Uplink configu- Switch-pointSubframe number ration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U UD S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 msD S U U U D D D D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D DD D 6 5 ms D S U U U D S U U D

Referring to Table 1, in each subframe of the radio frame, ‘D’represents a subframe for a DL transmission, ‘U’ represents a subframefor UL transmission, and ‘S’ represents a special subframe includingthree types of fields including a Downlink Pilot Time Slot (DwPTS), aGuard Period (GP), and a Uplink Pilot Time Slot (UpPTS).

A DwPTS is used for an initial cell search, synchronization or channelestimation in a UE. A UpPTS is used for channel estimation in an eNB andfor synchronizing a UL transmission synchronization of a UE. A GP isduration for removing interference occurred in a UL owing to multi-pathdelay of a DL signal between a UL and a DL.

Each subframe i includes slot 2i and slot 2i+1 of T_slot=15360*T_s=0.5ms.

The UL-DL configuration may be classified into 7 types, and the positionand/or the number of a DL subframe, a special subframe and a UL subframeare different for each configuration.

A point of time at which a change is performed from downlink to uplinkor a point of time at which a change is performed from uplink todownlink is called a switching point. The periodicity of the switchingpoint means a cycle in which an uplink subframe and a downlink subframeare changed is identically repeated. Both 5 ms and 10 ms are supportedin the periodicity of a switching point. If the periodicity of aswitching point has a cycle of a 5 ms downlink-uplink switching point,the special subframe S is present in each half frame. If the periodicityof a switching point has a cycle of a 5 ms downlink-uplink switchingpoint, the special subframe S is present in the first half frame only.

In all the configurations, 0 and 5 subframes and a DwPTS are used foronly downlink transmission. An UpPTS and a subframe subsequent to asubframe are always used for uplink transmission.

Such uplink-downlink configurations may be known to both an eNB and UEas system information. An eNB may notify UE of a change of theuplink-downlink allocation state of a radio frame by transmitting onlythe index of uplink-downlink configuration information to the UEwhenever the uplink-downlink configuration information is changed.Furthermore, configuration information is kind of downlink controlinformation and may be transmitted through a Physical Downlink ControlChannel (PDCCH) like other scheduling information. Configurationinformation may be transmitted to all UEs within a cell through abroadcast channel as broadcasting information.

Table 2 represents configuration (length of DwPTS/GP/UpPTS) of a specialsubframe.

TABLE 2 Normal cyclic prefix in downlink Extended cyclic prefix indownlink Special UpPTS UpPTS subframe Normal cyclic Extended cyclicNormal cyclic Extended cyclic configuration DwPTS prefix in uplinkprefix in uplink DwPTS prefix in uplink prefix in uplink 0  6592 · T_(s)2192 · T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 119760 · T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 ·T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 ·T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 ·T_(s) 23040 · T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

The structure of a radio subframe according to the example of FIG. 1 isjust an example, and the number of subcarriers included in a radioframe, the number of slots included in a subframe and the number of OFDMsymbols included in a slot may be changed in various manners.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin a wireless communication system to which an embodiment of the presentinvention may be applied.

Referring to FIG. 2, one downlink slot includes a plurality of OFDMsymbols in a time domain. It is described herein that one downlink slotincludes 7 OFDMA symbols and one resource block includes 12 subcarriersfor exemplary purposes only, and the present invention is not limitedthereto.

Each element on the resource grid is referred to as a resource element,and one resource block (RB) includes 12×7 resource elements. The numberof RBs N̂DL included in a downlink slot depends on a downlinktransmission bandwidth.

The structure of an uplink slot may be the same as that of a downlinkslot.

FIG. 3 shows the structure of a downlink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 3, a maximum of three OFDM symbols located in a frontportion of a first slot of a subframe correspond to a control region inwhich control channels are allocated, and the remaining OFDM symbolscorrespond to a data region in which a physical downlink shared channel(PDSCH) is allocated. Downlink control channels used in 3GPP LTEinclude, for example, a physical control format indicator channel(PCFICH), a physical downlink control channel (PDCCH), and a physicalhybrid-ARQ indicator channel (PHICH).

A PCFICH is transmitted in the first OFDM symbol of a subframe andcarries information about the number of OFDM symbols (i.e., the size ofa control region) which is used to transmit control channels within thesubframe. A PHICH is a response channel for uplink and carries anacknowledgement (ACK)/not-acknowledgement (NACK) signal for a HybridAutomatic Repeat Request (HARQ). Control information transmitted in aPDCCH is called Downlink Control Information (DCI). DCI includes uplinkresource allocation information, downlink resource allocationinformation, or an uplink transmission (Tx) power control command for aspecific UE group.

A PDCCH may carry information about the resource allocation andtransport format of a downlink shared channel (DL-SCH) (this is alsocalled an “downlink grant”), resource allocation information about anuplink shared channel (UL-SCH) (this is also called a “uplink grant”),paging information on a PCH, system information on a DL-SCH, theresource allocation of a higher layer control message, such as a randomaccess response transmitted on a PDSCH, a set of transmission powercontrol commands for individual UE within specific UE group, and theactivation of a Voice over Internet Protocol (VoIP), etc. A plurality ofPDCCHs may be transmitted within the control region, and UE may monitora plurality of PDCCHs. A PDCCH is transmitted on a single ControlChannel Element (CCE) or an aggregation of some contiguous CCEs. A CCEis a logical allocation unit that is used to provide a PDCCH with acoding rate according to the state of a radio channel. A CCE correspondsto a plurality of resource element groups. The format of a PDCCH and thenumber of available bits of a PDCCH are determined by an associationrelationship between the number of CCEs and a coding rate provided byCCEs.

An eNB determines the format of a PDCCH based on DCI to be transmittedto UE and attaches a Cyclic Redundancy Check (CRC) to controlinformation. A unique identifier (a Radio Network Temporary Identifier(RNTI)) is masked to the CRC depending on the owner or use of a PDCCH.If the PDCCH is a PDCCH for specific UE, an identifier unique to the UE,for example, a Cell-RNTI (C-RNTI) may be masked to the CRC. If the PDCCHis a PDCCH for a paging message, a paging indication identifier, forexample, a Paging-RNTI (P-RNTI) may be masked to the CRC. If the PDCCHis a PDCCH for system information, more specifically, a SystemInformation Block (SIB), a system information identifier, for example, aSystem Information-RNTI (SI-RNTI) may be masked to the CRC. A RandomAccess-RNTI (RA-RNTI) may be masked to the CRC in order to indicate arandom access response which is a response to the transmission of arandom access preamble by UE.

FIG. 4 shows the structure of an uplink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 4, the uplink subframe may be divided into a controlregion and a data region in a frequency domain. A physical uplinkcontrol channel (PUCCH) carrying uplink control information is allocatedto the control region. A physical uplink shared channel (PUSCH) carryinguser data is allocated to the data region. In order to maintain singlecarrier characteristic, one UE does not send a PUCCH and a PUSCH at thesame time.

A Resource Block (RB) pair is allocated to a PUCCH for one UE within asubframe. RBs belonging to an RB pair occupy different subcarriers ineach of 2 slots. This is called that an RB pair allocated to a PUCCH isfrequency-hopped in a slot boundary.

Multi-Input Multi-Output (MIMO)

A MIMO technology does not use single transmission antenna and singlereception antenna that have been commonly used so far, but uses amulti-transmission (Tx) antenna and a multi-reception (Rx) antenna. Inother words, the MIMO technology is a technology for increasing acapacity or enhancing performance using multi-input/output antennas inthe transmission end or reception end of a wireless communicationsystem. Hereinafter, MIMO is called a “multi-input/output antenna.”.

More specifically, the multi-input/output antenna technology does notdepend on a single antenna path in order to receive a single totalmessage and completes total data by collecting a plurality of datapieces received through several antennas. As a result, themulti-input/output antenna technology can increase a data transfer ratewithin a specific system range and can also increase a system rangethrough a specific data transfer rate.

It is expected that an efficient multi-input/output antenna technologywill be used because next-generation mobile communication requires adata transfer rate much higher than that of existing mobilecommunication. In such a situation, the MIMO communication technology isa next-generation mobile communication technology which may be widelyused in mobile communication UE and a relay node and has been in thespotlight as a technology which may overcome a limit to the transferrate of another mobile communication attributable to the expansion ofdata communication.

Meanwhile, the multi-input/output antenna (MIMO) technology of varioustransmission efficiency improvement technologies that are beingdeveloped has been most in the spotlight as a method capable ofsignificantly improving a communication capacity andtransmission/reception performance even without the allocation ofadditional frequencies or a power increase.

FIG. 5 shows the configuration of a known MIMO communication system.

Referring to FIG. 5, if the number of transmission (Tx) antennas isincreased to N_T and the number of reception (Rx) antennas is increasedto N_R at the same time, a theoretical channel transmission capacity isincreased in proportion to the number of antennas, unlike in the casewhere a plurality of antennas is used only in a transmitter or areceiver. Accordingly, a transfer rate can be improved, and frequencyefficiency can be significantly improved. In this case, a transfer rateaccording to an increase of a channel transmission capacity may betheoretically increased by a value obtained by multiplying the followingrate increment R_i by a maximum transfer rate R_o if one antenna isused.

R _(i)=min(N _(T) ,N _(R))  [Equation 1]

That is, in an MIMO communication system using 4 transmission antennasand 4 reception antennas, for example, a quadruple transfer rate can beobtained theoretically compared to a single antenna system.

Such a multi-input/output antenna technology may be divided into aspatial diversity method for increasing transmission reliability usingsymbols passing through various channel paths and a spatial multiplexingmethod for improving a transfer rate by sending a plurality of datasymbols at the same time using a plurality of transmission antennas.Furthermore, active research is being recently carried out on a methodfor properly obtaining the advantages of the two methods by combiningthe two methods.

Each of the methods is described in more detail below.

First, the spatial diversity method includes a space-time blockcode-series method and a space-time Trelis code-series method using adiversity gain and a coding gain at the same time. In general, theTrelis code-series method is better in terms of bit error rateimprovement performance and the degree of a code generation freedom,whereas the space-time block code-series method has low operationalcomplexity. Such a spatial diversity gain may correspond to an amountcorresponding to the product (N_T×N_R) of the number of transmissionantennas (N_T) and the number of reception antennas (N_R).

Second, the spatial multiplexing scheme is a method for sendingdifferent data streams in transmission antennas. In this case, in areceiver, mutual interference is generated between data transmitted by atransmitter at the same time. The receiver removes the interferenceusing a proper signal processing scheme and receives the data. A noiseremoval method used in this case may include a Maximum LikelihoodDetection (MLD) receiver, a Zero-Forcing (ZF) receiver, a Minimum MeanSquare Error (MMSE) receiver, Diagonal-Bell Laboratories LayeredSpace-Time (D-BLAST), and Vertical-Bell Laboratories Layered Space-Time(V-BLAST). In particular, if a transmission end can be aware of channelinformation, a Singular Value Decomposition (SVD) method may be used.

Third, there is a method using a combination of a spatial diversity andspatial multiplexing. If only a spatial diversity gain is to beobtained, a performance improvement gain according to an increase of adiversity disparity is gradually saturated. If only a spatialmultiplexing gain is used, transmission reliability in a radio channelis deteriorated. Methods for solving the problems and obtaining the twogains have been researched and may include a double space-time transmitdiversity (double-STTD) method and a space-time bit interleaved codedmodulation (STBICM).

In order to describe a communication method in a multi-input/outputantenna system, such as that described above, in more detail, thecommunication method may be represented as follows through mathematicalmodeling.

First, as shown in FIG. 5, it is assumed that N_T transmission antennasand NR reception antennas are present.

First, a transmission signal is described below. If the N_T transmissionantennas are present as described above, a maximum number of pieces ofinformation which can be transmitted are N_T, which may be representedusing the following vector.

s=[s ₁ ,s ₂ ,Λ,s _(N) _(T) ]^(T)  [Equation 2]

Meanwhile, transmission power may be different in each of pieces oftransmission information s_1, s_2, . . . , s_NT. In this case, if piecesof transmission power are P_1, P_2, . . . , P_NT, transmissioninformation having controlled transmission power may be representedusing the following vector.

ŝ=[ŝ ₁ ,ŝ ₂ ,Λ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ ,Λ,P _(N) _(T) s_(N) _(T) ]^(T)  [Equation 3]

Furthermore, transmission information having controlled transmissionpower in the Equation 3 may be represented as follows using the diagonalmatrix P of transmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & O & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\M \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Meanwhile, the information vector having controlled transmission powerin the Equation 4 is multiplied by a weight matrix W, thus forming N_Ttransmission signals x_1, x_2, . . . , x_NT that are actuallytransmitted. In this case, the weight matrix functions to properlydistribute the transmission information to antennas according to atransport channel condition. The following may be represented using thetransmission signals x_1, x_2, . . . , x_NT.

$\begin{matrix}{x = {\begin{bmatrix}x_{1} \\x_{2} \\M \\x_{i} \\M \\x_{N_{T}}\end{bmatrix} = {{\begin{bmatrix}w_{11} & w_{12} & \Lambda & w_{1N_{T}} \\w_{21} & w_{22} & \Lambda & w_{12_{T}} \\M & \; & O & \; \\w_{i\; 1} & w_{i\; 2} & \Lambda & w_{{iN}_{T}} \\M & \; & O & \; \\w_{N_{T}1} & w_{N_{T}2} & \Lambda & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\M \\{\hat{s}}_{j} \\M \\s_{{\hat{N}}_{T}}\end{bmatrix}} = {{W\; \hat{s}} = {WPs}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In this case, w_ij denotes weight between an i-th transmission antennaand a j-th transmission information, and W is an expression of a matrixof the weight. Such a matrix W is called a weight matrix or precodingmatrix.

Meanwhile, the transmission signal x, such as that described above, maybe considered to be used in a case where a spatial diversity is used anda case where spatial multiplexing is used.

If spatial multiplexing is used, all the elements of the informationvector s have different values because different signals are multiplexedand transmitted. In contrast, if the spatial diversity is used, all theelements of the information vector s have the same value because thesame signals are transmitted through several channel paths.

A method of mixing spatial multiplexing and the spatial diversity may betaken into consideration. In other words, the same signals may betransmitted using the spatial diversity through 3 transmission antennas,for example, and the remaining different signals may be spatiallymultiplexed and transmitted.

If N_R reception antennas are present, the reception signals y_1, y_2, .. . , y_NR of the respective antennas are represented as follows using avector y.

y=[y ₁ ,y ₂ ,Λ,y _(N) _(R) ]^(T)  [Equation 6]

Meanwhile, if channels in a multi-input/output antenna communicationsystem are modeled, the channels may be classified according totransmission/reception antenna indices. A channel passing through areception antenna i from a transmission antenna j is represented ash_ij. In this case, it is to be noted that in order of the index ofh_ij, the index of a reception antenna comes first and the index of atransmission antenna then comes.

Several channels may be grouped and expressed in a vector and matrixform. For example, a vector expression is described below.

FIG. 6 is a diagram showing a channel from a plurality of transmissionantennas to a single reception antenna.

As shown in FIG. 6, a channel from a total of N_T transmission antennasto a reception antenna i may be represented as follows.

h _(i) ^(T) =[h _(i1) ,h _(i2) ,Λ,h _(iN) _(T) ]  [Equation 7]

Furthermore, if all channels from the N_T transmission antenna to NRreception antennas are represented through a matrix expression, such asEquation 7, they may be represented as follows.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\M \\h_{i}^{T} \\M \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \Lambda & h_{1N_{T}} \\h_{21} & h_{22} & \Lambda & h_{2N_{T}} \\M & \; & O & \; \\h_{i\; 1} & h_{i\; 2} & \Lambda & h_{{iN}_{T}} \\M & \; & O & \; \\h_{N_{R}1} & h_{N_{R}2} & \Lambda & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Meanwhile, Additive White Gaussian Noise (AWGN) is added to an actualchannel after the actual channel experiences the channel matrix H.Accordingly, AWGN n_1, n_2, . . . , n_NR added to the N_R receptionantennas, respectively, are represented using a vector as follows.

n=[n ₁ ,n ₂ ,Λ,n _(N) _(R) ]^(T)  [Equation 9]

A transmission signal, a reception signal, a channel, and AWGN in amulti-input/output antenna communication system may be represented tohave the following relationship through the modeling of the transmissionsignal, reception signal, channel, and AWGN, such as those describedabove.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\M \\y_{i} \\M \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \Lambda & h_{1N_{T}} \\h_{21} & h_{22} & \Lambda & h_{2N_{T}} \\M & \; & O & \; \\h_{i\; 1} & h_{i\; 2} & \Lambda & h_{{iN}_{T}} \\M & \; & O & \; \\h_{N_{R}1} & h_{N_{R}2} & \Lambda & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\M \\x_{j} \\M \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\M \\n_{i} \\M \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

Meanwhile, the number of rows and columns of the channel matrix Hindicative of the state of channels is determined by the number oftransmission/reception antennas. In the channel matrix H, as describedabove, the number of rows becomes equal to the number of receptionantennas N_R, and the number of columns becomes equal to the number oftransmission antennas N_T. That is, the channel matrix H becomes anN_R×N_T matrix.

In general, the rank of a matrix is defined as a minimum number of thenumber of independent rows or columns. Accordingly, the rank of thematrix is not greater than the number of rows or columns. As for figuralstyle, for example, the rank H of the channel matrix H is limited asfollows.

rank(H)≥min(N _(T) ,N _(R))  [Equation 11]

Furthermore, if a matrix is subjected to Eigen value decomposition, arank may be defined as the number of Eigen values that belong to Eigenvalues and that are not 0. Likewise, if a rank is subjected to SingularValue Decomposition (SVD), it may be defined as the number of singularvalues other than 0. Accordingly, the physical meaning of a rank in achannel matrix may be said to be a maximum number on which differentinformation may be transmitted in a given channel.

In this specification, a “rank” for MIMO transmission indicates thenumber of paths through which signals may be independently transmittedat a specific point of time and a specific frequency resource. The“number of layers” indicates the number of signal streams transmittedthrough each path. In general, a rank has the same meaning as the numberof layers unless otherwise described because a transmission end sendsthe number of layers corresponding to the number of ranks used in signaltransmission.

Reference Signal (RS)

In a wireless communication system, a signal may be distorted duringtransmission because data is transmitted through a radio channel. Inorder for a reception end to accurately receive a distorted signal, thedistortion of a received signal needs to be corrected using channelinformation. In order to detect channel information, a method ofdetecting channel information using the degree of the distortion of asignal transmission method and a signal known to both the transmissionside and the reception side when they are transmitted through a channelis chiefly used. The aforementioned signal is called a pilot signal orreference signal (RS).

Furthermore recently, when most of mobile communication systems transmita packet, they use a method capable of improving transmission/receptiondata efficiency by adopting multiple transmission antennas and multiplereception antennas instead of using one transmission antenna and onereception antenna used so far. When data is transmitted and receivedusing multiple input/output antennas, a channel state between thetransmission antenna and the reception antenna must be detected in orderto accurately receive the signal. Accordingly, each transmission antennamust have an individual reference signal.

In a mobile communication system, an RS may be basically divided intotwo types depending on its object. There are an RS having an object ofobtaining channel state information and an RS used for datademodulation. The former has an object of obtaining, by a UE, to obtainchannel state information in the downlink. Accordingly, a correspondingRS must be transmitted in a wideband, and a UE must be capable ofreceiving and measuring the RS although the UE does not receive downlinkdata in a specific subframe. Furthermore, the former is also used forradio resources management (RRM) measurement, such as handover. Thelatter is an RS transmitted along with corresponding resources when aneNB transmits the downlink. A UE may perform channel estimation byreceiving a corresponding RS and thus may demodulate data. Thecorresponding RS must be transmitted in a region in which data istransmitted.

A downlink RS includes one common RS (CRS) for the acquisition ofinformation about a channel state shared by all of UEs within a cell andmeasurement, such as handover, and a dedicated RS (DRS) used for datademodulation for only a specific UE. Information for demodulation andchannel measurement can be provided using such RSs. That is, the DRS isused for only data demodulation, and the CRS is used for the two objectsof channel information acquisition and data demodulation.

The reception side (i.e., UE) measures a channel state based on a CRSand feeds an indicator related to channel quality, such as a channelquality indicator (Cal), a precoding matrix index (PMI) and/or a rankindicator (RI), back to the transmission side (i.e., an eNB). The CRS isalso called a cell-specific RS. In contrast, a reference signal relatedto the feedback of channel state information (CSI) may be defined as aCSI-RS.

The DRS may be transmitted through resource elements if data on a PDSCHneeds to be demodulated. A UE may receive information about whether aDRS is present through a higher layer, and the DRS is valid only if acorresponding PDSCH has been mapped. The DRS may also be called aUE-specific RS or demodulation RS (DMRS).

FIG. 7 illustrates reference signal patterns mapped to downlink resourceblock pairs in a wireless communication system to which the presentinvention may be applied.

Referring to FIG. 7, a downlink resource block pair, that is, a unit inwhich a reference signal is mapped, may be represented in the form ofone subframe in a time domain×12 subcarriers in a frequency domain. Thatis, in a time axis (an x axis), one resource block pair has a length of14 OFDM symbols in the case of a normal cyclic prefix (CP) (FIG. 7a )and has a length of 12 OFDM symbols in the case of an extended cyclicprefix (CP) (FIG. 7b ). In the resource block lattice, resource elements(REs) indicated by “0”, “1”, “2”, and “3” mean the locations of the CRSsof antenna port indices “0”, “1”, “2”, and “3”, respectively, and REsindicated by “D” mean the location of a DRS.

A CRS is described in more detail below. The CRS is a reference signalwhich is used to estimate the channel of a physical antenna and may bereceived by all UEs located within a cell in common. The CRS isdistributed to a full frequency bandwidth. That is, the CRS iscell-specific signal and is transmitted every subframe in a wideband.Furthermore, the CRS may be used for channel quality information (CSI)and data demodulation.

A CRS is defined in various formats depending on an antenna array on thetransmitting side (eNB). In the 3GPP LTE system (e.g., Release-8), an RSfor a maximum four antenna ports is transmitted depending on the numberof transmission antennas of an eNB. The side from which a downlinksignal is transmitted has three types of antenna arrays, such as asingle transmission antenna, two transmission antennas and fourtransmission antennas. For example, if the number of transmissionantennas of an eNB is two, CRSs for a No. 0 antenna port and a No. 1antenna port are transmitted. If the number of transmission antennas ofan eNB is four, CRSs for No. 0˜No. 3 antenna ports are transmitted. Ifthe number of transmission antennas of an eNB is four, a CRS pattern inone RB is shown in FIG. 7.

If an eNB uses a single transmission antenna, reference signals for asingle antenna port are arrayed.

If an eNB uses two transmission antennas, reference signals for twotransmission antenna ports are arrayed using a time divisionmultiplexing (TDM) scheme and/or a frequency division multiplexing (FDM)scheme. That is, different time resources and/or different frequencyresources are allocated in order to distinguish between referencesignals for two antenna ports.

Furthermore, if an eNB uses four transmission antennas, referencesignals for four transmission antenna ports are arrayed using the TDMand/or FDM schemes. Channel information measured by the reception side(i.e., UE) of a downlink signal may be used to demodulate datatransmitted using a transmission scheme, such as single transmissionantenna transmission, transmission diversity, closed-loop spatialmultiplexing, open-loop spatial multiplexing or amulti-user-multi-input/output (MIMO) antenna.

If a multi-input multi-output antenna is supported, when a RS istransmitted by a specific antenna port, the RS is transmitted in thelocations of resource elements specified depending on a pattern of theRS and is not transmitted in the locations of resource elementsspecified for other antenna ports. That is, RSs between differentantennas do not overlap.

A DRS is described in more detail below. The DRS is used to demodulatedata. In multi-input multi-output antenna transmission, precoding weightused for a specific UE is combined with a transmission channeltransmitted by each transmission antenna when the UE receives an RS, andis used to estimate a corresponding channel without any change.

A 3GPP LTE system (e.g., Release-8) supports a maximum of fourtransmission antennas, and a DRS for rank 1 beamforming is defined. TheDRS for rank 1 beamforming also indicates an RS for an antenna portindex 5.

In an LTE-A system, that is, an advanced and developed form of the LTEsystem, the design is necessary to support a maximum of eighttransmission antennas in the downlink of an eNB. Accordingly, RSs forthe maximum of eight transmission antennas must be also supported. Inthe LTE system, only downlink RSs for a maximum of four antenna portshas been defined. Accordingly, if an eNB has four to a maximum of eightdownlink transmission antennas in the LTE-A system, RSs for theseantenna ports must be additionally defined and designed. Regarding theRSs for the maximum of eight transmission antenna ports, theaforementioned RS for channel measurement and the aforementioned RS fordata demodulation must be designed.

One of important factors that must be considered in designing an LTE-Asystem is backward compatibility, that is, that an LTE UE must welloperate even in the LTE-A system, which must be supported by the system.From an RS transmission viewpoint, in the time-frequency domain in whicha CRS defined in LTE is transmitted in a full band every subframe, RSsfor a maximum of eight transmission antenna ports must be additionallydefined. In the LTE-A system, if an RS pattern for a maximum of eighttransmission antennas is added in a full band every subframe using thesame method as the CRS of the existing LTE, RS overhead is excessivelyincreased.

Accordingly, the RS newly designed in the LTE-A system is basicallydivided into two types, which include an RS having a channel measurementobject for the selection of MCS or a PMI (channel state information-RSor channel state indication-RS (CSI-RS)) and an RS for the demodulationof data transmitted through eight transmission antennas (datademodulation-RS (DM-RS)).

The CSI-RS for the channel measurement object is characterized in thatit is designed for an object focused on channel measurement unlike theexisting CRS used for objects for measurement, such as channelmeasurement and handover, and for data demodulation. Furthermore, theCSI-RS may also be used for an object for measurement, such as handover.The CSI-RS does not need to be transmitted every subframe unlike the CRSbecause it is transmitted for an object of obtaining information about achannel state. In order to reduce overhead of a CSI-RS, the CSI-RS isintermittently transmitted on the time axis.

For data demodulation, a DM-RS is dedicatedly transmitted to a UEscheduled in a corresponding time-frequency domain. That is, a DM-RS fora specific UE is transmitted only in a region in which the correspondingUE has been scheduled, that is, in the time-frequency domain in whichdata is received.

In the LTE-A system, a maximum of eight transmission antennas aresupported in the downlink of an eNB. In the LTE-A system, if RSs for amaximum of eight transmission antennas are transmitted in a full bandevery subframe using the same method as the CRS in the existing LTE, RSoverhead is excessively increased. Accordingly, in the LTE-A system, anRS has been separated into the CSI-RS of the CSI measurement object forthe selection of MCS or a PMI and the DM-RS for data demodulation, andthus the two RSs have been added. The CSI-RS may also be used for anobject, such as RRM measurement, but has been designed for a main objectfor the acquisition of CSI. The CSI-RS does not need to be transmittedevery subframe because it is not used for data demodulation.Accordingly, in order to reduce overhead of the CSI-RS, the CSI-RS isintermittently transmitted on the time axis. That is, the CSI-RS has aperiod corresponding to a multiple of the integer of one subframe andmay be periodically transmitted or transmitted in a specifictransmission pattern. In this case, the period or pattern in which theCSI-RS is transmitted may be set by an eNB.

For data demodulation, a DM-RS is dedicatedly transmitted to a UEscheduled in a corresponding time-frequency domain. That is, a DM-RS fora specific UE is transmitted only in the region in which scheduling isperformed for the corresponding UE, that is, only in the time-frequencydomain in which data is received.

In order to measure a CSI-RS, a UE must be aware of information aboutthe transmission subframe index of the CSI-RS for each CSI-RS antennaport of a cell to which the UE belongs, the location of a CSI-RSresource element (RE) time-frequency within a transmission subframe, anda CSI-RS sequence.

In the LTE-A system, an eNB has to transmit a CSI-RS for each of amaximum of eight antenna ports. Resources used for the CSI-RStransmission of different antenna ports must be orthogonal. When one eNBtransmits CSI-RSs for different antenna ports, it may orthogonallyallocate the resources according to the FDM/TDM scheme by mapping theCSI-RSs for the respective antenna ports to different REs.Alternatively, the CSI-RSs for different antenna ports may betransmitted according to the CDM scheme for mapping the CSI-RSs topieces of code orthogonal to each other.

When an eNB notifies a UE belonging to the eNB of information on aCSI-RS, first, the eNB must notify the UE of information about atime-frequency in which a CSI-RS for each antenna port is mapped.Specifically, the information includes subframe numbers in which theCSI-RS is transmitted or a period in which the CSI-RS is transmitted, asubframe offset in which the CSI-RS is transmitted, an OFDM symbolnumber in which the CSI-RS RE of a specific antenna is transmitted,frequency spacing, and the offset or shift value of an RE in thefrequency axis.

A CSI-RS is transmitted through one, two, four or eight antenna ports.Antenna ports used in this case are p=15, p=15, 16, p=15, . . . , 18,and p=15, . . . , 22, respectively. A CSI-RS may be defined for only asubcarrier interval Δf=15 kHz.

In a subframe configured for CSI-RS transmission, a CSI-RS sequence ismapped to a complex-valued modulation symbol a_k,l̂(p) used as areference symbol on each antenna port p as in Equation 12.

$\begin{matrix}{\mspace{79mu} {{a_{k,l}^{(p)} = {w_{l^{''}} \cdot {r_{l,n_{s}}\left( m^{\prime} \right)}}}{k = {k^{\prime} + {12\; m} + \left\{ {{\begin{matrix}{- 0} & {{{{for}\mspace{14mu} p} \in \left\{ {15,16} \right\}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 6} & {{{{for}\mspace{14mu} p} \in \left\{ {17,18} \right\}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 1} & {{{{for}\mspace{14mu} p} \in \left\{ {19,20} \right\}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 7} & {{{{for}\mspace{14mu} p} \in \left\{ {21,22} \right\}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 0} & {{{{for}\mspace{14mu} p} \in \left\{ {15,16} \right\}},{{extended}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 3} & {{{{for}\mspace{14mu} p} \in \left\{ {17,18} \right\}},{{extended}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 6} & {{{{for}\mspace{14mu} p} \in \left\{ {19,20} \right\}},{{extended}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 9} & {{{{for}\mspace{14mu} p} \in \left\{ {21,22} \right\}},{{extended}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}}\end{matrix}l} = {l^{\prime} + \left\{ {{\begin{matrix}l^{''} & \begin{matrix}{{{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{14mu} {configurations}\mspace{14mu} 0} - 19},} \\{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}\end{matrix} \\{2l^{''}} & \begin{matrix}{{{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{14mu} {configurations}\mspace{14mu} 20} - 31},} \\{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}\end{matrix} \\l^{''} & \begin{matrix}{{{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{14mu} {configurations}\mspace{14mu} 0} - 27},} \\{{extended}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}\end{matrix}\end{matrix}\mspace{79mu} w_{l^{''}}} = \left\{ {{{\begin{matrix}1 & {p \in \left\{ {15,17,19,21} \right\}} \\\left( {- 1} \right)^{l^{''}} & {p \in \left\{ {16,18,20,22} \right\}}\end{matrix}\mspace{79mu} l^{''}} = {{0,1\mspace{79mu} m} = 0}},1,\ldots \;,{{N_{RB}^{DL} - {1\mspace{79mu} m^{\prime}}} = {m + \left\lfloor \frac{N_{RB}^{\max,{DL}} - N_{RB}^{DL}}{2} \right\rfloor}}} \right.} \right.}} \right.}}}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

In Equation 12, (k′,l′) (wherein k′ is a subcarrier index within aresource block and l′ indicates an OFDM symbol index within a slot.) andthe condition of n_s is determined depending on a CSI-RS configuration,such as Table 3 or Table 4.

Table 3 illustrates the mapping of (k′,I′) from a CSI-RS configurationin a normal CP.

TABLE 3 Number of CSI reference signals configured CSI reference 1 or 24 8 signal n_(s) n_(s) n_(s) configuration (k′, l′) mod 2 (k′, l′) mod 2(k′, l′) mod 2 Frame structure 0 (9, 5) 0 (9, 5) 0 (9, 5) 0 type 1 and 21 (11, 2)  1 (11, 2)  1 (11, 2)  1 2 (9, 2) 1 (9, 2) 1 (9, 2) 1 3 (7, 2)1 (7, 2) 1 (7, 2) 1 4 (9, 5) 1 (9, 5) 1 (9, 5) 1 5 (8, 5) 0 (8, 5) 0 6(10, 2)  1 (10, 2)  1 7 (8, 2) 1 (8, 2) 1 8 (6, 2) 1 (6, 2) 1 9 (8, 5) 1(8, 5) 1 10 (3, 5) 0 11 (2, 5) 0 12 (5, 2) 1 13 (4, 2) 1 14 (3, 2) 1 15(2, 2) 1 16 (1, 2) 1 17 (0, 2) 1 18 (3, 5) 1 19 (2, 5) 1 Frame structure20 (11, 1)  1 (11, 1)  1 (11, 1)  1 type 2 only 21 (9, 1) 1 (9, 1) 1(9, 1) 1 22 (7, 1) 1 (7, 1) 1 (7, 1) 1 23 (10, 1)  1 (10, 1)  1 24(8, 1) 1 (8, 1) 1 25 (6, 1) 1 (6, 1) 1 26 (5, 1) 1 27 (4, 1) 1 28 (3, 1)1 29 (2, 1) 1 30 (1, 1) 1 31 (0, 1) 1

Table 4 illustrates the mapping of (k′,l′) from a CSI-RS configurationin an extended CP.

TABLE 4 Number of CSI reference signals configured CSI reference 1 or 24 8 signal n_(s) n_(s) n_(s) configuration (k′, l′) mod 2 (k′, l′) mod 2(k′, l′) mod 2 Frame structure 0 (11, 4)  0 (11, 4)  0 (11, 4) 0 type 1and 2 1 (9, 4) 0 (9, 4) 0  (9, 4) 0 2 (10, 4)  1 (10, 4)  1 (10, 4) 1 3(9, 4) 1 (9, 4) 1  (9, 4) 1 4 (5, 4) 0 (5, 4) 0 5 (3, 4) 0 (3, 4) 0 6(4, 4) 1 (4, 4) 1 7 (3, 4) 1 (3, 4) 1 8 (8, 4) 0 9 (6, 4) 0 10 (2, 4) 011 (0, 4) 0 12 (7, 4) 1 13 (6, 4) 1 14 (1, 4) 1 15 (0, 4) 1 Framestructure 16 (11, 1)  1 (11, 1)  1 (11, 1) 1 type 2 only 17 (10, 1)  1(10, 1)  1 (10, 1) 1 18 (9, 1) 1 (9, 1) 1  (9, 1) 1 19 (5, 1) 1 (5, 1) 120 (4, 1) 1 (4, 1) 1 21 (3, 1) 1 (3, 1) 1 22 (8, 1) 1 23 (7, 1) 1 24(6, 1) 1 25 (2, 1) 1 26 (1, 1) 1 27 (0, 1) 1

Referring to Table 3 and Table 4, in the transmission of a CSI-RS, inorder to reduce inter-cell interference (ICI) in a multi-cellenvironment including a heterogeneous network (HetNet) environment, amaximum of 32 different configurations (in the case of a normal CP) or amaximum of 28 different configurations (in the case of an extended CP)are defined.

The CSI-RS configuration is different depending on the number of antennaports and a CP within a cell, and a neighboring cell may have a maximumof different configurations. Furthermore, the CSI-RS configuration maybe divided into a case where it is applied to both an FDD frame and aTDD frame and a case where it is applied to only a TDD frame dependingon a frame structure.

(k′,l′) and n_s are determined depending on a CSI-RS configuration basedon Table 3 and Table 4, and time-frequency resources used for CSI-RStransmission are determined depending on each CSI-RS antenna port.

FIG. 8 is a diagram illustrating resources to which reference signalsare mapped in a wireless communication system to which the presentinvention may be applied.

FIG. 8(a) shows twenty types of CSI-RS configurations available forCSI-RS transmission by one or two CSI-RS antenna ports, FIG. 8(b) showsten types of CSI-RS configurations available for four CSI-RS antennaports, and FIG. 8(c) shows five types of CSI-RS configurations availablefor eight CSI-RS antenna ports.

As described above, radio resources (i.e., an RE pair) in which a CSI-RSis transmitted are determined depending on each CSI-RS configuration.

If one or two antenna ports are configured for CSI-RS transmission withrespect to a specific cell, the CSI-RS is transmitted on radio resourceson a configured CSI-RS configuration of the twenty types of CSI-RSconfigurations shown in FIG. 8(a).

Likewise, when four antenna ports are configured for CSI-RS transmissionwith respect to a specific cell, a CSI-RS is transmitted on radioresources on a configured CSI-RS configuration of the ten types ofCSI-RS configurations shown in FIG. 8(b). Furthermore, when eightantenna ports are configured for CSI-RS transmission with respect to aspecific cell, a CSI-RS is transmitted on radio resources on aconfigured CSI-RS configuration of the five types of CSI-RSconfigurations shown in FIG. 8(c).

A CSI-RS for each antenna port is subjected to CDM for every two antennaports (i.e., {15,16}, {17,18}, {19,20} and {21,22}) on the same radioresources and transmitted. For example, in the case of antenna ports 15and 16, CSI-RS complex symbols for the respective antenna ports 15 and16 are the same, but are multiplied by different types of orthogonalcode (e.g., Walsh code) and mapped to the same radio resources. Thecomplex symbol of the CSI-RS for the antenna port 15 is multiplied by[1, 1], and the complex symbol of the CSI-RS for the antenna port 16 ismultiplied by [1 −1] and mapped to the same radio resources. The same istrue of the antenna ports {17,18}, {19,20} and {21,22}.

A UE may detect a CSI-RS for a specific antenna port by multiplying codeby which a transmitted symbol has been multiplied. That is, atransmitted symbol is multiplied by the code [1 1] multiplied in orderto detect the CSI-RS for the antenna port 15, and a transmitted symbolis multiplied by the code [1 −1] multiplied in order to detect theCSI-RS for the antenna port 16.

Referring to FIGS. 8(a) to 8(c), in the case of the same CSI-RSconfiguration index, radio resources according to a CSI-RS configurationhaving a large number of antenna ports include radio resources having asmall number of CSI-RS antenna ports. For example, in the case of aCSI-RS configuration 0, radio resources for the number of eight antennaports include both radio resources for the number of four antenna portsand radio resources for the number of one or two antenna ports.

A plurality of CSI-RS configurations may be used in one cell. 0 or oneCSI-RS configuration may be used for a non-zero power (NZP) CSI-RS, and0 or several CSI-RS configurations may be used for a zero power (ZP)CSI-RS.

For each bit set to 1 in a zeropower (ZP) CSI-RS (‘ZeroPowerCSI-RS) thatis a bitmap of 16 bits configured by a high layer, a UE assumes zerotransmission power in REs (except a case where an RE overlaps an REassuming a NZP CSI-RS configured by a high layer) corresponding to thefour CSI-RS columns of Table 3 and Table 4. The most significant bit(MSB) corresponds to the lowest CSI-RS configuration index, and nextbits in the bitmap sequentially correspond to next CSI-RS configurationindices.

A CSI-RS is transmitted only in a downlink slot that satisfies thecondition of (n_s mod 2) in Table 3 and Table 4 and a subframe thatsatisfies the CSI-RS subframe configurations.

In the case of the frame structure type 2 (TDD), a CSI-RS is nottransmitted in a special subframe, a synchronization signal (SS), asubframe colliding against a PBCH or SystemInformationBlockType1 (SIB 1)Message transmission or a subframe configured to paging messagetransmission.

Furthermore, an RE in which a CSI-RS for any antenna port belonging toan antenna port set S (S={15}, S={15,16}, S={17,18}, S={19,20} orS={21,22}) is transmitted is not used for the transmission of a PDSCH orfor the CSI-RS transmission of another antenna port.

Time-frequency resources used for CSI-RS transmission cannot be used fordata transmission. Accordingly, data throughput is reduced as CSI-RSoverhead is increased. By considering this, a CSI-RS is not configuredto be transmitted every subframe, but is configured to be transmitted ineach transmission period corresponding to a plurality of subframes. Inthis case, CSI-RS transmission overhead can be significantly reducedcompared to a case where a CSI-RS is transmitted every subframe.

A subframe period (hereinafter referred to as a “CSI transmissionperiod”) T_CSI-RS and a subframe offset Δ_CSI-RS for CSI-RS transmissionare shown in Table 5.

Table 5 illustrates CSI-RS subframe configurations.

TABLE 5 CSI-RS-SubframeConfig CSI-RS periodicity CSI-RS subframe offsetI_(CSI-RS) T_(CSI-RS) (subframes) Δ_(CSI-RS) (subframes) 0-4 5I_(CSI-RS)  5-14 10 I_(CSI-RS) − 5  15-34 20 I_(CSI-RS) − 15 35-74 40I_(CSI-RS) − 35  75-154 80 I_(CSI-RS) − 75

Referring to Table 5, the CSI-RS transmission period T_CSI-RS and thesubframe offset Δ_CSI-RS are determined depending on the CSI-RS subframeconfiguration I_CSI-RS.

The CSI-RS subframe configuration of Table 5 may be configured as one ofthe aforementioned ‘SubframeConfig’ field and‘zeroTxPowerSubframeConfig’ field. The CSI-RS subframe configuration maybe separately configured with respect to an NZP CSI-RS and a ZP CSI-RS.

A subframe including a CSI-RS satisfies Equation 13.

(10n _(f) +└n _(s)/2┘−Δ_(CSI-RS))mod T _(CSI-RS)=0  [Equation 13]

In Equation 13, T_CSI-RS means a CSI-RS transmission period, Δ_CSI-RSmeans a subframe offset value, n_f means a system frame number, and n_smeans a slot number.

In the case of a UE in which the transmission mode 9 has been configuredwith respect to a serving cell, one CSI-RS resource configuration may beconfigured for the UE. In the case of a UE in which the transmissionmode 10 has been configured with respect to a serving cell, one or moreCSI-RS resource configuration (s) may be configured for the UE.

In the current LTE standard, a CSI-RS configuration includes an antennaport number (antennaPortsCount), a subframe configuration(subframeConfig), and a resource configuration (resourceConfig).Accordingly, the a CSI-RS configuration provides notification that aCSI-RS is transmitted how many antenna port, provides notification ofthe period and offset of a subframe in which a CSI-RS will betransmitted, and provides notification that a CSI-RS is transmitted inwhich RE location (i.e., a frequency and OFDM symbol index) in acorresponding subframe.

Specifically, the following parameters for each CSI-RS (resource)configuration are configured through high layer signaling.

-   -   If the transmission mode 10 has been configured, a CSI-RS        resource configuration identifier    -   A CSI-RS port number (antennaPortsCount): a parameter (e.g., one        CSI-RS port, two CSI-RS ports, four CSI-RS ports or eight CSI-RS        ports) indicative of the number of antenna ports used for CSI-RS        transmission    -   A CSI-RS configuration (resourceConfig) (refer to Table 3 and        Table 4): a parameter regarding a CSI-RS allocation resource        location    -   A CSI-RS subframe configuration (subframeConfig, that is,        I_CSI-RS) (refer to Table 5): a parameter regarding the period        and/or offset of a subframe in which a CSI-RS will be        transmitted    -   If the transmission mode 9 has been configured, transmission        power P_C for CSI feedback: in relation to the assumption of a        UE for reference PDSCH transmission power for feedback, when the        UE derives CSI feedback and takes a value within a [−8, 15] dB        range in a 1-dB step size, P_C is assumed to be the ratio of        energy per resource element (EPRE) per PDSCH RE and a CSI-RS        EPRE.    -   If the transmission mode 10 has been configured, transmission        power P_C for CSI feedback with respect to each CSI process. If        CSI subframe sets C_CSI,0 and C_CSI,1 are configured by a high        layer with respect to a CSI process, P_C is configured for each        CSI subframe set in the CSI process.    -   A pseudo-random sequence generator parameter n_ID    -   If the transmission mode 10 has been configured, a high layer        parameter ‘qcl-CRS-Info-r11’ including a QCL scrambling        identifier for a quasico-located (QCL) type B UE assumption        (qcl-ScramblingIdentity-r11), a CRS port count        (crs-PortsCount-r11), and an MBSFN subframe configuration list        (mbsfn-SubframeConfigList-r11) parameter.

When a CSI feedback value derived by a UE has a value within the [−8,15] dB range, P_C is assumed to be the ration of PDSCH EPRE to CSI-RSEPRE. In this case, the PDSCH EPRE corresponds to a symbol in which theratio of PDSCH EPRE to CRS EPRE is ρ_A.

A CSI-RS and a PMCH are not configured in the same subframe of a servingcell at the same time.

In the frame structure type 2, if four CRS antenna ports have beenconfigured, a CSI-RS configuration index belonging to the [20-31] set(refer to Table 3) in the case of a normal CP or a CSI-RS configurationindex belonging to the [16-27] set (refer to Table 4) in the case of anextended CP is not configured in a UE.

A UE may assume that the CSI-RS antenna port of a CSI-RS resourceconfiguration has a QCL relation with delay spread, Doppler spread,Doppler shift, an average gain and average delay.

A UE in which the transmission mode 10 and the QCL type B have beenconfigured may assume that antenna ports 0-3 corresponding to a CSI-RSresource configuration and antenna ports 15-22 corresponding to a CSI-RSresource configuration have QCL relation with Doppler spread and Dopplershift.

In the case of a UE in which the transmission modes 1-9 have beenconfigured, one ZP CSI-RS resource configuration may be configured inthe UE with respect to a serving cell. In the case of a UE in which thetransmission mode 10 has been configured, one or more ZP CSI-RS resourceconfigurations may be configured in the UE with respect to a servingcell.

The following parameters for a ZP CSI-RS resource configuration may beconfigured through high layer signaling.

-   -   The ZP CSI-RS configuration list (zeroTxPowerResourceConfigList)        (refer to Table 3 and Table 4): a parameter regarding a        zero-power CSI-RS configuration    -   The ZP CSI-RS subframe configuration (eroTxPowerSubframeConfig,        that is, I_CSI-RS) (refer to Table 5): a parameter regarding the        period and/or offset of a subframe in which a zero-power CSI-RS        is transmitted

A ZP CSI-RS and a PMCH are not configured in the same subframe of aserving cell at the same time.

In the case of a UE in which the transmission mode 10 has beenconfigured, one or more channel state information-interferencemeasurement (CSI-IM) resource configurations may be configured in the UEwith respect to a serving cell.

The following parameters for each CSI-IM resource configuration may beconfigured through high layer signaling.

-   -   The ZP CSI-RS configuration (refer to Table 3 and Table 4)    -   The ZP CSI RS subframe configuration I_CSI-RS (refer to Table 5)

A CSI-IM resource configuration is the same as any one of configured ZPCSI-RS resource configurations.

A CSI-IM resource and a PMCH are not configured within the same subframeof a serving cell at the same time.

Massive MIMO

A MIMO system having a plurality of antennas may be called a massive

MIMO system and has been in the spotlight as means for improvingspectrum efficiency, energy efficiency and processing complexity.

In recent 3GPP, in order to satisfy the requirements of spectrumefficiency for a future mobile communication system, a discussion aboutthe massive MIMO system has started. The massive MIMO is also calledfull-dimension MIMO (FD-MIMO).

In a wireless communication system after LTE Release (Rel)-12, theintroduction of an active antenna system (AAS) is considered.

Unlike the existing passive antenna system in which an amplifier andantenna capable of adjusting the phase and size of a signal have beenseparated, the AAS means a system in which each antenna is configured toinclude an active element, such as an amplifier.

The AAS does not require a separate cable, connector and other hardwarefor connecting an amplifier and an antenna because the active antenna isused, and thus has a high efficiency characteristic in terms of energyand operating costs. In particular, the AAS enables an advanced MIMOtechnology, such as the formation of an accurate beam pattern or 3D beampattern in which a beam direction and a beam width are consideredbecause the AAS supports each electronic beam control method.

Due to the introduction of an advanced antenna system, such as the AAS,a massive MIMO structure having a plurality of input/output antennas anda multi-dimension antenna structure is also considered. For example,unlike in the existing straight type antenna array, if a two-dimensional(2D) antenna array is formed, a 3D beam pattern can be formed by theactive antenna of the AAS.

FIG. 9 illustrates a 2D-AAS having 64 antenna elements in a wirelesscommunication system to which the present invention may be applied.

FIG. 9 illustrates a common 2D antenna array. A case where N_t=N_v·N_hantennas has a square form as in FIG. 9 may be considered. In this case,N_h indicates the number of antenna columns in a horizontal direction,and N_v indicates the number of antenna rows in a vertical direction.

If the antenna array of such a 2D structure is used, radio waves can becontrolled both in the vertical direction (elevation) and the horizontaldirection (azimuth) so that a transmission beam can be controlled in the3D space. A wavelength control mechanism of such a type may be called 3Dbeamforming.

FIG. 10 illustrates a system in which an eNB or UE has a plurality oftransmission/reception antennas capable of forming a 3D beam based onthe AAS in a wireless communication system to which the presentinvention may be applied.

FIG. 10 is a diagram of the aforementioned example and illustrates a 3DMIMO system using a 2D antenna array (i.e., 2D-AAS).

From the point of view of a transmission antenna, if a 3D beam patternis used, a semi-static or dynamic beam can be formed in the verticaldirection of the beam in addition to the horizontal direction. Forexample, an application, such as the formation of a sector in thevertical direction, may be considered.

Furthermore, from the point of view of a reception antenna, when areception beam is formed using a massive reception antenna, a signalpower rise effect according to an antenna array gain may be expected.Accordingly, in the case of the uplink, an eNB can receive a signal froma UE through a plurality of antennas. In this case, there is anadvantage in that the UE can set its transmission power very low byconsidering the gain of the massive reception antenna in order to reducean interference influence.

FIG. 11 illustrates a 2D antenna system having cross-polarizations in awireless communication system to which the present invention may beapplied.

A 2D planar antenna array model in which polarization is considered maybe diagrammed as shown in FIG. 11.

Unlike the existing MIMO system according to a passive antenna, a systembased on an active antenna can dynamically control the gain of anantenna element by applying weight to an active element (e.g., anamplifier) to which each antenna element has been attached (orincluded). The antenna system may be modeled in an antenna element levelbecause a radiation pattern depends on the number of antenna elementsand an antenna arrangement, such as antenna spacing.

An antenna array model, such as the example of FIG. 11, may berepresented by (M, N, P). This corresponds to a parameter thatcharacterizes an antenna array structure.

M indicates the number of antenna elements having the same polarizationin each column (i.e., the vertical direction) (i.e., the number ofantenna elements having a +45° slant in each column or the number ofantenna elements having a −45° slant in each column).

N indicates the number of columns in the horizontal direction (i.e., thenumber of antenna elements in the horizontal direction).

P indicates the number of dimensions of polarization. P=2 in the case ofcross-polarization as in the case of FIG. 11, or P=1 in the case ofco-polarization.

An antenna port may be mapped to a physical antenna element. The antennaport may be defined by a reference signal related to a correspondingantenna port. For example, in the LTE system, the antenna port 0 may berelated to a cell-specific reference signal (CRS), and the antenna port6 may be related to a positioning reference signal (PRS).

For example, an antenna port and a physical antenna element may bemapped in a one-to-one manner. This may correspond to a case where asingle cross-polarization antenna element is used for downlink MIMO ordownlink transmit diversity. For example, the antenna port 0 is mappedto one physical antenna element, whereas the antenna port 1 may bemapped to the other physical antenna element. In this case, from thepoint of view of a UE, two types of downlink transmission are present.One is related to a reference signal for the antenna port 0, and theother is related to a reference signal for the antenna port 1.

For another example, a single antenna port may be mapped to multiplephysical antenna elements. This may correspond to a case where a singleantenna port is used for beamforming. In beamforming, multiple physicalantenna elements are used, so downlink transmission may be directedtoward a specific UE. In general, this may be achieved using an antennaarray configured using multiple columns of multiple cross-polarizationantenna elements. In this case, from the point of view of a UE, one typeof downlink transmission generated from a single antenna port ispresent. One is related to a CRS for the antenna port 0, and the otheris related to a CRS for the antenna port 1.

That is, an antenna port indicates downlink transmission from the pointof view of a UE not actual downlink transmission from a physical antennaelement by an eN B.

For another example, a plurality of antenna ports is used for downlinktransmission, but each antenna port may be mapped to multiple physicalantenna elements. This may correspond to a case where an antenna arrayis used for downlink MIMO or downlink diversity. For example, each ofthe antenna ports 0 and 1 may be mapped to multiple physical antennaelements. In this case, from the point of view of a UE, two types ofdownlink transmission. One is related to a reference signal for theantenna port 0, and the other is related to a reference signal for theantenna port 1.

In FD-MIMO, the MIMO precoding of a data stream may experience antennaport virtualization, transceiver unit (or a transmission and receptionunit) (TXRU) virtualization, and an antenna element pattern.

In the antenna port virtualization, a stream on an antenna port isprecoded on a TXRU. In the TXRU virtualization, a TXRU signal isprecoded on an antenna element. In the antenna element pattern, a signalradiated by an antenna element may have a directional gain pattern.

In the existing transceiver modeling, a static one-to-one mappingbetween an antenna port and a TXRU is assumed, and a TXRU virtualizationeffect is joined into a static (TXRU) antenna pattern including theeffects of the TXRU virtualization and the antenna element pattern.

The antenna port virtualization may be performed by afrequency-selective method. In LTE, an antenna port, together with areference signal (or pilot), is defined. For example, for precoded datatransmission on an antenna port, a DMRS is transmitted in the samebandwidth as a data signal, and both the DMRS and data are precoded bythe same precoder (or the same TXRU virtualization precoding). For CSImeasurement, a CSI-RS is transmitted through multiple antenna ports. InCSI-RS transmission, a precoder that characterizes mapping between aCSI-RS port and a TXRU may be designed in a unique matrix so that a UEcan estimate a TXRU virtualization precoding matrix for a data precodingvector.

A TXRU virtualization method is discussed in 1D TXRU virtualization and2D TXRU virtualization, which are described below with reference to thefollowing drawing.

FIG. 12 illustrates a transceiver unit model in a wireless communicationsystem to which the present invention may be applied.

In the 1D TXRU virtualization, M_TXRU TXRUs are related to M antennaelements configured in a single column antenna array having the samepolarization.

In the 2D TXRU virtualization, a TXRU model configuration correspondingto the antenna array model configuration (M, N, P) of FIG. 11 may berepresented by (M_TXRU, N, P). In this case, M_TXRU means the number ofTXRUs present in the 2D same column and same polarization, and alwayssatisfies M_TXRU≤M.

That is, the total number of TXRUs is the same as M_TXRU×N×P.

A TXRU virtualization model may be divided into a TXRU virtualizationmodel option-1: sub-array partition model as in FIG. 12(a) and a TXRUvirtualization model option-2: full connection model as in FIG. 12(b)depending on a correlation between an antenna element and a TXRU.

Referring to FIG. 12(a), in the case of the sub-array partition model,an antenna element is partitioned into multiple antenna element groups,and each TXRU is connected to one of the groups.

Referring to FIG. 12(b), in the case of the full-connection model, thesignals of multiple TXRUs are combined and transferred to a singleantenna element (or the arrangement of antenna elements).

In FIG. 12, q is the transmission signal vectors of antenna elementshaving M co-polarizations within one column. W is a wideband TXRUvirtualization vector, and W is a wideband TXRU virtualization matrix. Xis the signal vectors of M_TXRU TXRUs.

In this case, mapping between an antenna port and TXRUs may beone-to-one or one-to-many.

In FIG. 12, mapping between a TXRU and an antenna element(TXRU-to-element mapping) shows one example, but the present inventionis not limited thereto. From the point of view of hardware, the presentinvention may be identically applied to mapping between an TXRU and anantenna element which may be implemented in various forms.

Method of Transmitting or Receiving Channel State Information

A CSI process may be configured as two classes, such as CSI report ClassA and CSI report Class B.

In the case of Class A, a UE may report CSI according to W=W1·W2codebook based on {8, 12, 16} CSI-RS antenna ports.

In the case of Class B, a UE may report L port CSI, assuming one of thefollowing four schemes.

Scheme 1: An indicator for a beam selection and an L port CQI/PMI/RI fora selected beam. A total number of configured ports over all of CSI-RSresources within a CSI process are greater than L.

Scheme 2: An L port precoder from a codebook into which both a beamselection(s) and co-phasing are incorporated in two polarizations. Atotal number of configured antenna ports within a CSI process are L.

Scheme 3: A codebook into which an L port CSI for a selected beam and abeam selection are incorporated. A total number of configured ports isgreater than L in all of CSI-RS resources within a CSI process.

Scheme 4: An L port CQI/PMI/RI. A total number of configured portswithin a CSI process is L. If a CSI measurement restriction issupported, the L port CQI/PMI/RI is always configured.

In this case, the beam selection means the selection of a subset ofantenna ports within one CSI-RS resource or the selection of a CSI-RSresource from a set of resources.

Furthermore, the CSI process is related to a K CSI-RSresource/configuration with an N_k port for a k-th CSI-RS resource (inthis case, K may be equal to or greater than 1).

The present invention proposes a method regarding a signalingtransmission or reception method for configuring a CSI-RS when multipleCSI-RS resources, such as a non-precoded CSI-RS or a beamformedCSI-RS-based technology, are configured in a multiple antenna MIMOsystem (e.g., FD-MIMO or a massive MIMO system).

For example, if a non-precoded CSI-RS (i.e., Class A) is configured in aUE, a CSI-RS configuration of 12 ports (i.e., CSI-RS resources) may beconfigured by aggregating four CSI-RS configurations of 3 ports.

Furthermore, if a precoded CSI-RS (i.e., Class B) is configured in a UE,a plurality of CSI-RS resources (e.g., corresponding to each beam) maybe configured in the UE. For example, if a plurality of CSI processes isconfigured in a UE, a plurality of CSI-RS resources may be configured ineach CSI process. Furthermore, each CSI-RS resource may correspond toone beam and may include {1,2,4,8} antenna ports. The number of CSI-RSantenna ports in each of a plurality of CSI-RS resources configured in aUE may be differently configured.

When multiple CSI-RS resources are configured as described above, thepresent invention proposes a signaling method for solving ambiguitybetween the number of antenna ports (i.e., L ports) as a CSI-RS reportunit and the number of antenna ports (i.e., N_k) in the k-th resource ofK CSI-RS resources configured in a UE and an operating method of a UEassociated with the signaling method.

-   -   In the case of L=N_k

First, an operation into which the case of L=N_k is taken intoconsideration is described.

In accordance with an embodiment of the present invention, an eNB maytransmit information about L to a UE through high layer signaling (e.g.,RRC signaling). Accordingly, the eNB may assume that the UE is aspecific L-port CSI-RS and may notify the UE of a BI (or a CSI-RSresource indicator (CRI)) and/or an operation so that the UE performsthe operation, such as CSI feedback.

In this case, the L value may be configured as an additional parameterwithin a CSI process or may be delivered to the UE through separate highlayer signaling (e.g., RRC signaling). Alternatively, the L value may bepreviously defined as a specific value depending on a specifictransmission mode or configuration condition.

In accordance with another embodiment of the present invention, L is notexplicitly signaled and may be configured to be identical with an N_kport number for a CSI-RS resource. For example, the L may be implicitlydefined or may be configured in a UE so that a UE recognizes that theN_k port number is the same as the L within a specific CSI-RS resourceand performs an operation of performing a corresponding CSI report.Alternatively, the L may be implicitly defined or may be configured in aUE so that the UE recognizes that an N_k port number in a correspondingCSI-RS resource is the same as the L in each CSI-RS resource configuredin the UE and performs an operation of performing a corresponding CSIreport.

As described above, if the L value is explicitly signaled or implicitlysignaled so that it is the same as an N_k port number within a specificCSI-RS resource, a total number of CSI-RS ports corresponding to acorresponding CSI process may correspond to L_T=N_k×K=L×K. A UE mayselectively assume a CSI-RS port number, that is, the target of a CSIreport, in each CSI process through the L and the CSI-RS resource numberK.

For example, it is assumed that L=4 has been configured in a UE(explicit or implicit). In this case, the UE selectively recognizes thata unit of the number of CSI-RS ports, that is, the target of a CSIreport, in each CSI process, as 4 and may assume that corresponding{15,16,17,18} has been set as corresponding ports.

In this case, a restriction may have been applied to the L value so thatthe L value is configured from among specific predetermined candidatevalues, such as {1,2,4,6,8,12,16, . . . }, or a restriction may havebeen applied to the L value so that the L value is set from among L>=1.

-   -   In the case of L≠N_k

If in the given L value, L≠N_k with respect to a specific CSI-RSresource k, a CSI report operation of a UE regarding L≠N_k and a methodassuming a corresponding CSI-RS port for L≠N_k are as follows.

In this case, an eNB may notify a UE of the corresponding N_k (k=1, . .. , K) explicitly through high layer signaling (e.g., RRC signaling) orusing a bitmap with respect to all of the CSI resources of K.

In this case, a total number of CSI-RS ports become

$L_{T} = {\sum\limits_{k = 1}^{K}{N_{k}.}}$

In this case, if the L value and a port number N_k corresponding to aspecific CSI-RS resource k are different, there may be ambiguity whenthe UE performs port indexing and associated CSI derivation. In order tosolve such a problem, the present invention proposes a method in which aUE assumes the CSI-RS port and calculates associated CSI.

1. A UE first sequentially indexes a total port number L_T. For example,a case where a total number of CSI-RS resources K=4 and N_kcorresponding to each CSI-RS resource is {2,4,8,4} is taken intoconsideration. In this case, the total port number L_T is 18, and the UEmay configure or assume port indexing for each CSI-RS resource as or tobe {15,16}, {15,16,17,18}, {15,16,17,18,19,20,21,22}, {15,16,17,18}.

However, for example, if the number of antenna ports of a CSI-RS reportunit L=4 is configured in the UE, the UE may newly sequentially indexthe antenna ports in the total port number. For example, the UE maysequentially list the total number of 18 ports, and then may index thefour CSI-RS ports of them as follows. That is, the UE may (re)index theports as {15,16,17,18}, {15,16,17,18}, {15,16,17,18}, and {15,16,17,18}with respect to four CSI-RS resources, may derive CSI for each CSI-RSresource, and may feed it back to an eNB. Furthermore, the UE mayperform an operation of selecting a preferred CSI-RS resource from thefour CSI-RS resources and feeding it back to the eNB.

A. If the number of newly indexed ports is greater than the total portnumber (i.e., L×K>L_T), the UE may perform signaling for requesting achange of the number of CSI-RS resources K and/or the CSI-RS port numberL from the eNB.

Alternatively, the UE may not expect such signaling (i.e., signaling forL and K values in which the number of newly indexed ports is greaterthan the total port number). In this case, the operation of the UE maybe unspecified.

Alternatively, the last (or first) CSI-RS resource may be limited (orbound) so that it does not exceed the total port number. Furthermore, aCSI-RS port number of less than L may be assumed with respect to only acorresponding specific CSI-RS resource, and an operation, such as acorresponding CSI report, may be defined so that the UE performs theoperation or configured in the UE.

2. In another method, the UE may always assume

$L_{T} = {{\sum\limits_{k = 1}^{K}N_{k}} = L}$

and that the L-port is always the same as the sum of all of CSI-RS portswithin a corresponding CSI process, and may (re)index an L-porttherefor. Furthermore, the UE may derive CSI for the L-port with respectto each CSI-RS resource and feed it back to the eNB. Furthermore, the UEmay perform an operation of selecting a preferred CSI-RS resource fromthe total of CSI-RS resources and feeding it back to the eNB.

3. Definition may be performed so that the UE performs the CSI-RS port(re)indexing on a CSI-RS resource corresponding to a CSI-RS resource,that is, L=N_k, and performs an associated CSI report operation or sucha definition may be configured in the UE.

The above example, that is, a case where the total number of CSI-RSresources K=4 and N_k corresponding to each CSI-RS resource is {2,4,8,4}is taken into consideration. In this case, if L=4 is configured in theUE, a CSI-RS resource corresponding to L=N_k corresponds to the secondand fourth resources. Accordingly, the UE may (re)index ports as{15,16,17,18} with respect to only the second and fourth CSI-RSresources, may derive CSI for each CSI-RS resource, and may feed it backto the eNB. Furthermore, the UE may perform an operation of selecting apreferred CSI-RS resource from the second and fourth CSI-RS resourcesand feeding it back to the eNB.

4. Alternatively, if N_k configured in each CSI-RS resource is various,definition may be performed so that the UE assumes the value of thesmallest value N_k to be L, performs CSI-RS port (re)indexing, andperforms an associated CSI report operation or the definition may beconfigured in the UE.

The above example, that is, a case where the total number of CSI-RSresources K=4 and N_k corresponding to each CSI-RS resource is {2,4,8,4}is taken into consideration. In this case, a total port number L_T is18, and the UE may configure or assume port indexing for each CSI-RSresource as or to be {15,16}, {15,16,17,18}, {15,16,17,18,19,20,21,22},and {15,16,17,18}.

However, as in the present embodiment, if L=2 is configured in the UE,L=2 is greater than the L in the case of the second, third and fourthCSI resources, and thus the UE may newly and sequentially index portindexing with respect to a corresponding CSI resource. For example, inthe case of the second CSI resource, the UE may sequentially list thetotal number of 4 ports and configure them as two port indexing groups.That is, the UE may (re)index the 2 CSI-RS ports of {15, 16} and {15,16}, may derive CSI for each port indexing group, and may feed it backto the eNB. In other words, if one CSI-RS resource includes a pluralityof port indexing groups, the UE may derive CSI for each port indexinggroup and may feed CSI to the eNB for each port indexing group.Furthermore, the UE may perform an operation of selecting a preferredCSI-RS resource of a total of CSI-RS resources and feeding it back tothe eNB.

5. Alternatively, if N_k configured in each CSI-RS resource is various,definition may be defined so that the UE assumes the greatest value ofN_k to be L, performs CSI-RS port (re)indexing, and performs anassociated CSI report operation, or the definition may be configured inthe UE.

For example, a case where K=4 and a corresponding N_k is {4,4,8,4} istaken into consideration. In this case, a total port number L_T is 20,and the UE may configure or assume port indexing for respective CSI-RSresources as or to be {15,16,17,18}, {15,16,17,18},{15,16,17,18,19,20,21,22}, and {15,16,17,18}.

However, as in the present embodiment, if the UE sets L=8, L=8 issmaller than the L in the case of the first, second and fourth CSIresources, the UE may group the first and second CSI resources and(re)perform port indexing. For example, the UE may (re)perform portindexing as {15,16,17,18}+{15,16,17,18}={15,16,17,18,19,20,21,22}, mayderive CSI for each indexing, and may feed it back to the eNB. In otherwords, if a plurality of CSI-RS resources forms one port indexing group,the UE may derive CSI for a corresponding port indexing group and feedit back to the eNB. Furthermore, the UE may perform an operation ofselecting a preferred CSI-RS resource from the total of CSI-RS resourcesand feeding it back to the eNB.

A. In another embodiment, a case where K=4 and corresponding N_k is{2,4,8,4} is taken into consideration. In this case, a total port numberL_T is 18, and the UE may configure or assume port indexing forrespective CSI-RS resources as or to be {15,16}, {15,16,17,18},{15,16,17,18,19,20,21,22}, and {15,16,17,18}.

However, as in the present embodiment, if the UE sets L=8, the UE maysequentially (re)perform port indexing in all of CSI resources. The UEmay (re)index ports as {15,16,17,18,19,20,21,22},{15,16,17,18,19,20,21,22}, and {15,16}, may derive CSI for eachindexing, and may feed it back to the eNB. Furthermore, the UE mayperform an operation of selecting a preferred CSI-RS resource from thetotal of CSI-RS resources and feeding it back to the eNB.

B. Alternatively, port indexing may be (re)performed on only a CSIresource corresponding to L≠N_k. The above example, that is, if K=4 andcorresponding N_k is {2,4,8,4}, the UE may group the first, second andfourth CSI resources, may (re)index ports as {15,16,17,18,19,20,21,22}and {15,16}, may derive CSI for each indexing, and may feed it back tothe eNB. Furthermore, the UE may perform an operation of selecting apreferred CSI-RS resource from the total of CSI-RS resources and feedingit back to the eNB.

3. If a different L is configured depending on a beam index

A case where a different L is configured depending on a beam index istaken into consideration.

That is, in the state in which a CSI resource number K and a CSI-RS portnumber N_k in each resource on a CSI process configuration have beenconfigured in a UE, a separate beam number B and a CSI-RS port numberL_b for each beam may be additionally explicitly signaled. In this case,a total number of CSI-RS ports is

$L_{T} = {\sum\limits_{k = 1}^{K}{N_{k}.}}$

In this case, if the L_b value and N_k corresponding to a specificresource k are different, ambiguity is generated in the UE when the UEperforms port indexing and derives associated CSI. In order to solvethis problem, the present invention a method in which the UE assumes theCSI-RS port and calculates associated CSI.

The UE first sequentially indexes a total port number L_T. For example,a case where K=4 and the corresponding N_k is {2,4,8,4} is taken intoconsideration. In this case, the total port number L_T is 18, and the UEmay configure or assume port indexing for each CSI-RS resource as or tobe {15,16}, {15,16,17,18}, {15,16,17,18,19,20,21,22} and {15,16,17,18}.

However, for example, if L_b of {4,2,4,8} is configured in the UE, theUE may newly index port indexing sequentially from the total number ofports. For example, after the UE sequentially lists the total number of18 ports, the UE may index the four CSI-RS ports of the 18 ports asfollows. That is, the UE may (re)index the ports as {15,16,17,18},{15,16}, {15,16,17,18}, {15,16,17,18}, and {15,16,17,18,19,20,21,22}with respect to the four CSI-RS resources, may derive CSI for eachindexing, and may feed it back to an eNB. Furthermore, the UE mayperform an operation of selecting a preferred CSI-RS resource from thetotal of CSI-RS resources and feeding it back to the eNB.

A. If the number of ports that are newly (re)indexed is greater than thetotal port number, the UE may signal a request for a change of thenumber of CSI-RS resources K or the CSI-RS port number L_b to the eNB.

Alternatively, the UE may not expect such signaling (i.e., signaling forthe L_b and K value in which the number of newly indexed ports isgreater than the total port number). In this case, the operation of theUE may be unspecified.

Alternatively, the last (or first) CSI-RS resource may be limited (orbound) so that it does not exceed the total port number. Furthermore, aCSI-RS port number less than the greatest L_b value may be assumed withrespect to a corresponding specific CSI-RS resource, and definition maybe performed so that and the UE performs an operation, such as acorresponding CSI report, or such a definition may be configured in theUE.

FIG. 13 is a diagram illustrating a method of transmitting or receivingchannel state information according to an embodiment of the presentinvention.

Referring to FIG. 13, a UE receives information of one or more CSI-RSresources from an eNB (S1301).

In this case, the CSI-RS resource information may include the number ofantenna ports N_k for corresponding CSI-RS resources and resourceconfiguration information of a CSI-RS. In this case, if a plurality ofCSI processes is configured in the corresponding UE, information of oneor more CSI-RS resources in each CSI process may be transmitted to theUE.

The UE may receive information about the number of antenna ports L of aCSI-RS report unit from the eNB (S1302).

In this case, the UE may receive the number of beams configured in theUE and the number of antenna ports of a report unit of CSI configured inthe UE for each beam from the eNB.

In this case, the number of antenna ports L of a CSI-RS report unit, asdescribed above, may be configured to be identical with the number ofantenna ports within a specific CSI-RS resource among the one or moreCSI-RS resources configured in the UE. In this case, step S1302 may beomitted.

Furthermore, the information about the number of antenna ports L of aCSI-RS report unit (or information about the number of beams and thenumber of antenna ports of a CSI-RS report unit for each beam configuredin the UE) may be transmitted along with CSI-RS resource information ineach CSI process. That is, they may be transmitted at step S1301.

The UE receives a CSI-RS on the one or more antenna ports from the eNB(S1303).

The UE derives CSI based on the CSI-RS received through the CSI-RSresource (S1304).

In this case, the UE may assume a CSI-RS antenna port using the methodaccording to the embodiment of the present invention, and may derive theCSI.

when the number of antenna ports in each of one or more CSI-RS resources(e.g., at least any one of the number of antenna ports in each of one ormore CSI-RS resources) configured in the UE and the number of antennaports L of a report unit of the CSI configured in the UE are different,the UE may assume a CSI-RS antenna port based on the number of antennaports L of a report unit of the CSI configured in the UE, and may derivethe CSI based on the CSI-RS.

The UE may sequentially index a total number of antenna ports for atotal of CSI-RS resources configured in the UE using the number ofantenna ports L of a report unit of the CSI configured in the UE.

In this case, the number of antenna ports L of a report unit of the CSImay be configured to be identical with the smallest number of antennaports or the greatest number of antenna ports of the one or more CSI-RSresources configured in the UE.

If the product value of a total of CSI-RS resources K configured in theUE and the number of antenna ports L of a report unit of the CSIconfigured in the UE is greater than the total number of antenna portsfor the total of CSI-RS resources configured in the UE, the UE mayrequest the reconfiguration of the total number of CSI-RS resources Kconfigured in the UE and/or the number of antenna ports L of a reportunit of the CSI configured in the UE from the eNB.

Furthermore, the UE may assume that the total number of antenna portsfor the total of CSI-RS resources configured in the UE is the same asthe product value of the total of CSI-RS resources configured in the UEand the number of antenna ports of a report unit of the CSI configuredin the UE.

Furthermore, the UE may derive CSI for only a CSI-RS resource thatbelongs to the one or more CSI-RS resources configured in the UE andthat is the same as the number of antenna ports of a report unit of theCSI configured in the UE.

Furthermore, the UE may sequentially index the total number of antennaports for the total of CSI-RS resources configured in the UE using thenumber of antenna ports of a report unit of the CSI for each beamconfigured in the UE.

In this case, if the number of antenna ports of a CSI report unit forall of beams configured in the UE is greater than the total number ofantenna ports for the total of CSI-RS resources configured in the UE,the UE may request the reconfiguration of a total number of CSI-RSresources configured in the UE and/or the number of antenna ports of areport unit of the CSI for each beam configured in the UE from the eNB.

The UE reports the derived CSI to the eNB (S1305).

General Apparatus to which the Present Invention May be Applied

FIG. 14 illustrates a block diagram of a wireless communicationapparatus according to an embodiment of the present invention.

Referring to FIG. 14, the wireless communication system includes a basestation (eNB) 1410 and a plurality of user equipments (UEs) 1420 locatedwithin the region of the eNB 1410.

The eNB 1410 includes a processor 1411, a memory 1412 and a radiofrequency unit 1413. The processor 1411 implements the functions,processes and/or methods proposed in FIGS. 1 to 13 above. The layers ofwireless interface protocol may be implemented by the processor 1411.The memory 1412 is connected to the processor 1411, and stores varioustypes of information for driving the processor 1411. The RF unit 1413 isconnected to the processor 1411, and transmits and/or receives radiosignals.

The UE 1420 includes a processor 1421, a memory 1422 and a radiofrequency unit 1423. The processor 1421 implements the functions,processes and/or methods proposed in FIGS. 1 to 13 above. The layers ofwireless interface protocol may be implemented by the processor 1421.The memory 1422 is connected to the processor 1421, and stores varioustypes of information for driving the processor 1421. The RF unit 1423 isconnected to the processor 1421, and transmits and/or receives radiosignals.

The memories 1412 and 1422 may be located interior or exterior of theprocessors 1411 and 1421, and may be connected to the processors 1411and 1421 with well known means. In addition, the eNB 1410 and/or the UE1420 may have a single antenna or multiple antennas.

The embodiments described so far are those of the elements and technicalfeatures being coupled in a predetermined form. So far as there is notany apparent mention, each of the elements and technical features shouldbe considered to be selective. Each of the elements and technicalfeatures may be embodied without being coupled with other elements ortechnical features. In addition, it is also possible to construct theembodiments of the present invention by coupling a part of the elementsand/or technical features. The order of operations described in theembodiments of the present invention may be changed. A part of elementsor technical features in an embodiment may be included in anotherembodiment, or may be replaced by the elements and technical featuresthat correspond to other embodiment. It is apparent to constructembodiment by combining claims that do not have explicit referencerelation in the following claims, or to include the claims in a newclaim set by an amendment after application.

The embodiments of the present invention may be implemented by variousmeans, for example, hardware, firmware, software and the combinationthereof. In the case of the hardware, an embodiment of the presentinvention may be implemented by one or more application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), a processor, a controller, amicro controller, a micro processor, and the like.

In the case of the implementation by the firmware or the software, anembodiment of the present invention may be implemented in a form such asa module, a procedure, a function, and so on that performs the functionsor operations described so far. Software codes may be stored in thememory, and driven by the processor. The memory may be located interioror exterior to the processor, and may exchange data with the processorwith various known means.

It will be understood to those skilled in the art that variousmodifications and variations can be made without departing from theessential features of the inventions. Therefore, the detaileddescription is not limited to the embodiments described above, butshould be considered as examples. The scope of the present inventionshould be determined by reasonable interpretation of the attachedclaims, and all modification within the scope of equivalence should beincluded in the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention has been illustrated based on an example in whichthe present invention is applied to the 3GPP LTE/LTE-A systems, but maybe applied to various wireless communication systems in addition to the3GPP LTE/LTE-A systems.

1. A method for a user equipment (UE) to transmit channel stateinformation (CSI) in a wireless communication system, the methodcomprising: receiving a number of antenna ports in each of one or morechannel state information-reference signal (CSI-RS) resources configuredin the UE from an eNB; receiving, by the UE, a CSI-RS on one or moreantenna ports from the eNB; deriving the CSI based on the CSI-RS byassuming a CSI-RS antenna port based on a number of antenna ports of areport unit of the CSI configured in the UE, when the number of antennaports in each of one or more CSI-RSs configured in the UE and the numberof antenna ports of a report unit of the CSI configured in the UE aredifferent; and reporting the CSI to the eNB.
 2. The method of claim 1,further comprising: receiving information of the number of antenna portsof a report unit of the CSI from the eNB.
 3. The method of claim 1,wherein the number of antenna ports of a report unit of the CSI isconfigured to be identical with a number of antenna ports within aspecific CSI-RS resource of the one or more CSI-RS resources configuredin the UE.
 4. The method of claim 1, further comprising: sequentiallyindexing a total of antenna ports for a total of CSI-RS resourcesconfigured in the UE using the number of antenna ports of a report unitof the CSI configured in the UE.
 5. The method of claim 4, furthercomprising: requesting a reconfiguration of the total number of CSI-RSresources configured in the UE and/or the number of antenna ports of areport unit of the CSI configured in the UE from the eNB, when a productvalue of the total of CSI-RS resources configured in the UE and thenumber of antenna ports of a report unit of the CSI configured in the UEis greater than a total number of antenna ports for the total number ofCSI-RS resources configured in the UE.
 6. The method of claim 4, whereina product value of the total of CSI-RS resources configured in the UEand the number of antenna ports of a report unit of the CSI configuredin the UE is assumed to be identical with a total number of antennaports for the total number of CSI-RS resources configured in the UE. 7.The method of claim 4, wherein the number of antenna ports of a reportunit of the CSI is configured to be identical with a smallest number ofantenna ports of the one or more CSI-RS resources configured in the UE.8. The method of claim 4, wherein the number of antenna ports of areport unit of the CSI is configured to be identical with a greatestnumber of antenna ports of the one or more CSI-RS resources configuredin the UE.
 9. The method of claim 1, wherein the CSI is derived withrespect to only a CSI-RS resource that is identical with the number ofantenna ports of a report unit of the CSI configured in the UE among theone or more CSI-RS resources configured in the UE.
 10. The method ofclaim 1, further comprising: receiving a number of beams configured inthe UE and a number of antenna ports of a report unit of the CSIconfigured in the UE for each beam from the eNB.
 11. The method of claim10, further comprising a step of sequentially indexing a total ofantenna ports for a total of CSI-RS resources configured in the UE usinga number of antenna ports of a report unit of the CSI for each beamconfigured in the UE.
 12. The method of claim 11, further comprising astep of requesting a reconfiguration of the total number of CSI-RSresources configured in the UE and/or the number of antenna ports of areport unit of the CSI for each beam configured in the UE from the eNBif the number of antenna ports of a report unit of the CSI for the totalof beams configured in the UE is greater than the total number ofantenna ports for the total number of CSI-RS resources configured in theUE.
 13. A user equipment (UE) transmitting channel state information(CSI) in a wireless communication system, the UE comprising: a radiofrequency (RF) unit for transmitting or receiving a radio signal; and aprocessor controlling the RF unit, wherein the processor is configuredto: receive the number of antenna ports in each of one or more channelstate information-reference signal (CSI-RS) resources configured in theUE from an eNB, receive a CSI-RS on one or more antenna ports from theeNB, deriving the CSI based on the CSI-RS by assuming a CSI-RS antennaport based on the number of antenna ports of a report unit of the CSIconfigured in the UE, when the number of antenna ports in each of one ormore CSI-RSs configured in the UE and the number of antenna ports of areport unit of the CSI configured in the UE are different, and reportthe CSI to the eNB.